A. Field of the Invention
The invention relates to a method and a slurry suitable for use in treating a well penetrating an unconsolidated formation by emplacing a resin consolidated pack of particulate material adjacent the formation, and to a method of preparing the slurry.
B. Description of the Art
Production of detritus from unconsolidated, i.e. incompetent, subterranean formations producing valuable fluids, such as production of sand from an incompetent sandstone formation, is an ever present problem, particularly in the petroleum industry. A good discussion of the problem, and of the various techniques used to minimize concurrent production of such detritus can be found in an eight part series by George O. Suman, Jr., appearing in World Oil from November, 1974, through June, 1975. The series was published in 1975 as a reprint by Gulf Publishing Co. under the title "World Oil's Sand Control Handbook," the teachings of which are expressly incorporated herein. Three commonly used methods are (1) gravel packing, (2) plastic in situ consolidation, and (3) consolidated packing with a particulate material, often called consolidated gravel packing especially where the particulate material is sand. The latter technique is discussed in Part 7 of said Handbook, and it is this latter technique to which the present invention pertains.
In the early consolidated gravel packing art, typified by Henderson et al, U.S. Pat. No. 2,823,753, it was taught to coat a particulate with a resin, suspend the coated particulate in a suitable carrier, and inject the suspension into the borehole. Both oil based and aqueous based carriers were taught in the early literature (see, e.g. column 7, line 50 through column 8, line 5 of said U.S. Pat. No. 2,823,753), although as a practical matter, systems using aqueous carriers were never developed to the point of widespread commercial acceptance.
Precoated particulates had several drawbacks, however. Some precoated particulates were not sufficiently stable to be stored and transported without agglomeration. Others which could be handled without an objectionable degree of agglomeration suffered from an inability to form strong packs in low temperature wells, while stimultaneously maintaining adequate permeability. Consequently, efforts were generally concentrated on developing high particulate concentration oil based slurries which could be prepared without precoating the particulate prior to admixture with the carrier, and in maximizing the strength and permeability parameters of such systems.
Oil based systems, however, also suffer from numerous inherent disadvantages. In offshore operations, unused oil carried slurry must be transported back to shore, and even on land, disposal in an ecologically acceptable manner presents a problem. Purchasing the oil used as a carrier and carrying it in inventory adds cost to the treatment, particularly in periods of tight supply. Safety risks are somewhat greater with large quantities of combustible material at the well site. Some sources of brightstock oil have such high levels of cationic contaminants that poorly consolidated packs result even after treatments to neutralize at least partially the effect of such contaminants, such as by implementation of the teachings at column 4, line 60 et seq. of Copeland, U.S. Pat. No. 3,867,986. A further disadvantage of the oil carried systems is that the oil, which typically has a viscosity on the order of about 1000 centipoise at 80.degree. F, becomes considerably more viscous at lower surface temperatures, e.g. below 50.degree. F, making it difficult to handle. Also, well operators are reluctant to use oil carried systems in gas wells because of concern of possible formation damage by injection of heavy oil. Considerable friction loss is encountered in oil carried systems, making it difficult to fracture many formations without generating excessive pressures at the well head, so that the fracturing technique taught by Gurley et al. in U.S. Pat. No. 3,854,533 could not always be implemented safely. Finally, the sensitivity of oil-carried systems to water based fluids required careful handling prior to injection, and the use of oil as a displacing fluid or use of a wiper plug to separate the slurry from a water-based displacement fluid. These problems associated with oil carried systems can be avoided or at least ameliorated by practicing the present invention.